<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>

  <div id="app">
    姓：<input type="text" v-model="firstName"> +
    名：<input type="text" v-model="lastName"> =
    <span>{{ fullName }}</span><br><br>

    <button @click="changeName">改名卡</button>
  </div>
  <script src="./vue.js"></script>
  <script>
    const app = new Vue({
      el: '#app',
      data: {
        firstName: '刘',
        lastName: '备',
      },
      computed: {
        fullName: {
          get() {
            return this.firstName + this.lastName
          },
          set(value) {
            this.firstName = value.slice(0, 1)
            this.lastName = value.slice(1)
          }
        }
      },
      methods: {
        changeName() {
          this.fullName = '黄忠'
        }
      }
    })
  </script>
</body>

</html>